What are the chances that you were born a boy or a girl? Would you say a 100% chance? 50/50? What does that really mean? Let's use a penny as a model for gender selection. Think of heads as a girl and tails as a boy.
|Check It Out!|
|If you want to see for yourself, get a penny, paper, and something to write with. First, flip a penny 10 times and record the number of times it lands on heads and tails. Is it close to half the time for each? Now flip it 50 times and then 100 times. According to your data, after flipping a penny 100 times, what is the probability of having a girl? a boy? How does the data align with the predicted probability?|
If a penny had a head on each side instead of a head or tail, what would be the chance of getting heads when you flipped it? What is the chance you would get tails? You would get tails 0% of the time and heads 100% of the time. That translates to a probability of 0 for tails and a probability of 1 for heads. That's the same as saying the chance for having a girl is 100% and the chance for having a boy is 0%. So, probability is the chance of an event happening or not.
When you flip a normal coin, you have two possible outcomes, heads or tails. That means that for every time a coin is flipped, there's a 50% chance of its landing on heads and a 50% chance of its landing on tails. So, if you flipped a penny 100 times, the probability of landing on heads is 1/2, meaning it would be heads 50 times and tails the other 50. Does it always work out as exactly 50/50? Do parents with four children always have two girls and two boys?
The video below demonstrates how to determine probability of gender inheritance using a Punnett square instead of a penny.